This invention relates generally to a method and apparatus for preventing distortion in thin flanges subject to heat treatment during a repair process. Most aircraft engines have metallic structural parts with thin flanges that may include bolt holes and through slots. These types of structural parts are unique and very expensive. The problem with cracked and worn bolt holes is a very common type of degradation that occurs during regular engine operation. The use of heat treatment fixtures is often required when making repairs in order to reduce the risk of damage due to deformation. The concept and design of a heat treatment fixture must be carefully calculated to gain the expected results without any unexpected stress concentration.
Thin flanges with 75% of the area having bolt holes or through slots tend to distort over tolerance limits if subjected to heat treatment. In most cases, thin flanges have a face that mates with other parts and that requires a tight flatness tolerance. During manufacture such flanges include excess stock material, and final features are machined onto the flanges after heat treatment to avoid deformation. However, some repairs require high temperatures processes, such as welding, stress relief and brazing that will affect the finished thin flange tolerances and cause deformation. The use of heat treatment fixtures to restrain the deformation and keep the flange flat during high temperatures is well known, but a conventional heat treatment fixture requires bolts or clamps to keep the weight on the correct area of the flange. These bolts or clamps can cause other distortions by restraining small features of the part during growth of the part as a result of the heat treatment. Also, the process of tightening and un-tightening the bolts is labor consuming, requires considerable skill, and increases the cost of the repair.